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Stanford University Ph.D. Oral Examination
Plasmonic Optical Antennas
For Enhanced Light Detection and Emission
Edward S. Barnard
Stanford University
Department of Materials Science & Engineering
Advisor: Prof. Mark L. Brongersma
Wednesday April 6th 2011
3:30 pm
(Refreshments at 3:15 pm)
Location: Paul G. Allen Auditorium (CIS-X 101)
Antennas are used in a wide range of frequencies in the electromagnetic spectrum to concentrate
wave energy into electronic circuits. The principles that govern RF antennas can be applied to much
higher frequencies and be applied to produce nanoscale plasmonic antennas that act as “receivers”
and “transmitters” for visible light. This near-field concentration makes them excellent candidates for
light trapping in solar cells, light concentration in sub-wavelength photodetectors, or even localized
heating for cancer therapies. However the optical properties of metals at visible frequencies make it
difficult to apply traditional antenna design rules. Using full-field electromagnetic simulations and
analytical antenna models, we developed new design rules for producing optical antennas with a
desired set of optical properties. We then applied these design rules to create antennas that
resonantly enhance both absorption of thin silicon photodetectors and emission of cathodoluminescence (CL) photons. Through spatial and spectral mapping of both photocurrent and CL we
clearly show the fundamental and higher-order resonant modes of these antennas. With CL we are
also able to map the spatial distribution of these resonant modes with nanometer resolution. In
addition to these specific demonstrated applications, the results of this study enable optical engineers
to more easily design a myriad of plasmonic devices that employ optical antenna structures, including
nanoscale photodetectors, light sources, sensors, and modulators.